Method of pulverizing and mill therefor



Oct. 7!

D. V. SHERBAN METHOD OF PULIVERIZING, AND MILL THEREFOR nal Filed Dec. 23. 1921 2 sheets-sh; 2

INVENTOR M I was on. 7, 1924;

UNITED-STATES PATENT OFFICE.

DANIEL v. snnanam or can'ron, oino, ABSIGROB .ro THE nomlo'rcourm; or

' cmron, onro.

much. or- PULVERIZING AND uni. 'rmmnron.

' Original No. 1,427,234, dated August 29, 1922, Serial No. 594,524, filed. December 28, 1821. application for reissue fled larch 9, 1923. Serial No. 624,034.

To all whom it may concern:

Be it known that I, DANIEL V. SHERBA a citizen of the United- States, residin at Canton, in the county of Stark and k tate 6 of Ohio, have invented" certain new and useful Improvements in Methods of Pulverizing and Mills Therefor, of which the following is a specification.

Reduction of material in a pulverizing ,1 mill of the drum and ball type is effected in two ways, i. e. by raising the balls by tation of the drum to such a height that they will drop and strike the material lying on the bottom of the drum, and by movement of the balls relative to the charge and other balls. In other words, reduction is eifected by impact and attrition, both of which methods are ne'cessaryfor efiicient reduction. The efliciency of 'theimpact is dependent for a give'n size of balls on the distancewhich the balls drop and the length of drop' is dependent upon the height to which the balls are carried by the drumand this height is dependent on the rate of rotation 95 of the drum. As is well known, there is" little ifany attrition efiected in the portion of the char being carried u ward by. the

action of t e drum but is e ected by the rollingeand sliding of the portions which 80 have en carried up moving down along the surface of the upwardly moving'por- V tions of the charge. These two actions which are necessary to eflicienc cannot be obtained simultaneously in a b l and drum 1 type of mill as at resent constructed and operated, for the fo lowing reasons 2,-

To roduce eflicient impact action the drum ould be rotated at such a speed that when the upper portion ofthe ascending body reaches a lane, e..g. a plane indicated by the line a, b, Fig-urea, where avity overcomes centrifugal force, the e ements thereof will have sufiicient momentum to pass'beyond the inner surface of the as cending body so that'their downward movement will not be efiected or retarded by the-- On the otherhand efiecascendin body. tive attrition will result onl when the (164 see'nding elements of the ahargeroll and I slide over theascendin elements.

The invention descri herein has for its object the provision of an eflicient simul-' taneous reduction'of the material in a ball carrying off the fine dust, as it is produced,

from the interior of the drum, and for maintaining and protecting such means, together with various other features of construction and operation, as shall be more fully hereinafter descrmed.

In the drawings,

Figure 1 1s a view in-longitudinal sec- .tion, ;partly'in' elevation, showing a complete apparatus as assembled;

Figure 2 is a cross section on line IIII of Figure 1;

Figure 3 is a a. rotatable grinding barrel in cross section, showing the action of the balls within an uninterrupted area;

Figure 4 is a' si novel effect of introducing the interfering screen; and

diagrammatic view showing "lar view showing the Figure 5 IS an enlarged sectional detail I view of a portion of the central screen.

The mam operative member of the crushingap aratus consists of a rotatable drum or tum ling barrel 2, the heads or ends of which are mounted in suitable bearings 99 by means of the hollow trunnion extensions. 44. The receiving end of the drum communicates through one of said trunnion extensions with a supply pipe 5, to which lump coal is delivere b 6 leading from a hopper terminal orother source of supply. 'The conduit 5 has a valve controlled terminal 8 at any suitable inlet point for the reception of atmospheric air.

' The other head 3 is similar-l mountedby its trunnion 4 in the opposite by a suitable driving motor, adapted to colle'ct the dust as produced, and having a deconduit aring 9 and communicates throu h the said trunnion livery conduit 11 leading to a furnace or other 'pointof consumption or store The interior of the drum 2 may continuously 'openfrom end to end, or may be divided into a series of sectional compartments (1, b, respectively, divided by an an-- nular partition wall 12 extending transversely across the drum area-and serving to retain the series of crushing balls 13 in place. Longitudinal strips or abutments 14 extend at intervals. throughout the length of the inner circumference of the drum, in the manner of slats or ridges, and with" centrifugal force, have the function and effect of partially lifting the balls and dropping them as the drum rotates in carrying out its work of crushing and grindin the coal.

Extending inwardly through the central portion of the drum near its receiving end, is a cylindrical screen 15 communicating with the intake end of fan 10 through the trunnion 4 of the drum. The screen may be formed of comparatively fine mesh screen so as to prevent the passage 'therethrough of any particles of coal not sufficiently small to use as pulverized fuel, or may be otherwise made so as to admit to its interior only such fuel as is sufficiently fine to be utilized with an air feed column. In the drawings, the c linder is shown as of comparatively heavy s eet or late metaL'eXtending into the suction con uit at its delivery end and open for inflow of pulverized material throughout its length clear to the opposite end which is closed. Screen 15 is supported within the trunnion 4 by extended rods 16. Cylinder 15 V will be carried to a point where it will drop 'the 1 By interposin is provided throughout its body portion with series of longitudinally arranged slots or openings 17 comparatively narrow at their outer portions and enlarging inwardly by a Widening taper, as shown. By this means, the entrance opening controls the size of the fuel, and prevents a tendency to clog the slots.

The supply of air is preferably controlled through an. adjustably mounted air inlet valve 18 of easing suitably connected by rod 19 and a sheave-guided cord 20 with a rheo stat 21.

The function of the central screen 15 is two fold. It acts to collect by suction all of the sufficiently fine fuel as made and to carry it offthrough conduit 11, and also actsas a middle barrier for the crushing balls.

In mills of the usual construction portions of the charge, i. e. balls of material are carried upwardly by the slats or by centrifugal force or both a distance-dependent on the rate of rotation of the drum. If the rate of rotation is comparatively high the charge clear of the ascendin body of the diarge as shown in Figure 3. But if the rate of rotation is lower the charge -will.not have sufficient momentum to reach a int where it will have a free drop, and wi lroll or slide down the inner face of the ascending body. a barrier such as the screen 15 axially of t e drum and in the path of the fallin balls and material as in Figure 4, alling stream is divided into two branches passing downwardly on opposite sides of the barrier. Those balls which fall toward the main rising stream of balls at the ascending side of the drum are engaged frictionally thereby and the result is that a small cyclonic zone X is induced with a resulting rotary path of travel, "as indicated by the arrows. The effect is to greatly accelerate the grinding and pulverizing action,

and this action will be increased by using a mass of balls of varying size inthe common interior of the drum. The portion of the stream passingv to the left of the screen will have a free fall onto the portion of the charge on the bottom of the drum and will operate to crush the larger lumps'of the ma terial to a size more readily reduced by attritionwhen carried up to the cyclonic zone.

The impact of the balls on the screen will effect considerable reduction of the material. A further advantage is that the constant hammering of the balls on the central screen tends .to dislodge any adhering particles, thus keeping the slots 17 open and unobstructed.

By reference to Fig. 4 it will be seen that the diameter of the barrier relative to the diameter of the drum is of importance to produce effective reduction by attrition. Ex-

perience has shown that for a given diame ter of drum, sa 48 inches, the 'drum should be rotated at a out 28 revolutions er minute. The movements of the char e In such a drum having such a rate of rotation, no barrier being present, are clearly shown in Fig. 3, but by the interposition of a barrier, as 15, having such an external diameter a suflicint portion of the descending stream of material will be diverted to the right of the barrier as to fill the space between the barrier and the ascending body of material. Actual trial has shown that the barrier should have an external diameter not materially less than one-fourth and preferably about one-third of the internal diameter of the drum. In the construction shown herein, the barrier has an external diameter a little less than onethird of the internal diameterof the drum \Vhen the barrier and the drum. are so proportioned and the drum driven at about 28 revolutions per minute, the descending stream of the charge which falls clear of the ascending stream, will beso divided that the major portion thereof will pass to the right of the barrier-and maintain the space between the barrier and the ascending portion of the charge completely filled. By reason of the descending. movement of "a portion of the charge adjacentto the barrier and the ascending movement of the portion of the charge lying against thedrum, a cyclonic movement is produced. In order to insure effectiveness of this cyclonic movement of a portion of the charge, the space between the barrier and the ascending portion of the charge should be maintained in a filled condition which cannot be effected unless a barrier is formed of such proportion-that a large percentage of the stream falling clear of the ascending body is directed into the space between the ascending charge and the axis of the drum. 1 The space between the barrier 15 and the ascending portion of the char e may be likened to a hopper 'into whic material is diverted from the free falling stream in such uantities as not only to keep the hopper ful but to exert a substantial pressure by reason of the weight of the material to force the latter down through the hopper.

It is characteristic of the construction shown and described herein that as the portions of the char drop into the barrier, there will be a re uction of the material by impact. And further, as the charge, after striking upon the barrier and effecting an impact reduction, will slide and roll oil on both sides of the barrier and effect reduction by attrition. After the balls moving to the right of the barrier in Fig. 4 leave the same, they will roll down against the upwardly moving portions of the charge and efiect further reduction by attrition, and those falling to the left after leaving the barrier, will drop to the charge on the lower portion of the drum and effect reduction almost wholly by impact. Thus, it will be seen from the foregoing that by the interposition of a barrier in the stream falling clear of the upwardly moving body of the charge,

- auxiliary means for reduction by impact and attrition are provided.

It is charactertistic of the improvement claimed herein that the material and the air for removing reduced material enter through the same trunnion so that the air will assist in feeding the materialinto the drum and its distribution therein. It will be observed that the supply of 'material 'to and the flow of air through the drum are constant and'that by ad'usting the valve 18 the supply of air can varied in accordance with the grade of material which it is desired to remove from the drnm.

By reason of the forward pro 'ection of the charge from the u per end of t e ascending body, a ct is grmed in which no reduction wil be effected if a barrier is not employed. This ocket extends, as shown in ig. 3, vertical y to a considerable distance above the horizontal plane coincident with the axis of. the drum andhas such a widththat a portion will be in line with the hollow trunnions which form the inlets and.

outlets for the air and material. Hence, aconsiderable portion of the material would,

in the construction shown in Fig. 3, pass directly throu h the drum. But b employing a barrier suc as described and y directing a portion of the free-falling stream to the right of the barrier, the portion of the pocket a and also its dimensions are changed. 'Some of the portion of the charge included the screen.

-wardly 0 between a plane coincidin with the end of the screen and the end of t e drum will pass across the line and movement of the material and air entering the drum and prevent the direct flow of air into the pocket and thence into the tubular screen, such air will, however carry portions of the material entering t 1e drum and also portions of the charge moving across the open trunnion into the pockets and distribute it along the pocket if too coarse to pass through the openings in Some of the air will pass upwardl into the portion of the drum not occupie by the charge and must pass through the stream of the charge falling to the bottom of the drum before entering the outlet screen.

. The drum may be rotated in any suitable way, as b a pinion 22 engaging an annular rack 23, t e speed of rotation being suitably controlled by the driving gearing.

' The construction and operation of the invention will be readily understood, and appreciated from the foregoing description. The machine is capable of continuous and successful operation in the manner intended, without liability of getting out" of order,

and is well adapted'to perform its intended .functions in continuously ulverizing the coal and dehverlng the pu verized fuel in contmuousl uniform grade.

The mac ine may be built in differentsizes to suit local requirements, or variously changed in detail construction or otherwise by the skilled mechanic, but all such changes are to be considered as within the scope of the following claims. I

I claim herein as my invention 1. A grindin mill consisting of a rotatable drum provided with grinding balls and a central axially arranged suction screen having avcontinuous uninterrupted receiving cavity from one end to the other.

-2. A grinding mill consisting of. a rotatable druin rovided with grinding balls, a central axia ly arranged suction screen having a continuous uninterrupted receiving cavity from one end'to the other, means providing an extracting current therethrough, and means for introducing raw material to the drum.

3. In combination, .a rotatable drum, means for introducing raw material and air to one end thereof, a central axially arranged c lindrical screen extending inthe drum from the other end thereof having a continuous'uninterru ted receiving cavit from one end to the ot er, and a suction an and exhaust conduit conimunicating therewith.

4. In combination, a rotatable drum, means for introducing raw material and air to one end thereof, a centrally arranged c lindrical screen extending inwardly of t e drum from the other end thereof pro- Ill vided with inwardly enlarging circulation openings and a continuous interlor receiving cavity, and a suction fan and exhaust conduit communicating therewith.

5. In combination, a rotatable drum having' terminalhollow trunnions for inlet of raw material and air and outflow of pulverized material and air, a suction fan connected with the outflow trunnion, a central axially arranged suction screen extending from the outflow trunnion inwardly of the drum towards the receiving trunnion having a continuous open interior, means for supporting the screen, and a series of grinding balls in the drum.

6. The method herein described which consists in elevating a mass composedof vated portions 'ofthe mass to descend in separate streams one out of contact with the upwardly moving mass and one in contact therewith, whereby material of such ,inass is simultaneously pulverized by impact and attrition, causing a current of air to move in a direction substantially parallel with the axis of rotation of the mas and between the descending streams whereb i pulverized material may be removed throng such space between the streams'from' the charge. 7 7. The method herein described which consists in elevating a mass composed of material to be pulverized and crushing bodies, causing the elevated portion of the mass to descend in separate streams one in contact with the upwardly moving mass to eil'ect reduction by attrition and the other falling clear or out of contact with the upwardly moving mass, interposing a barrier in the path of the second stream wherebysuch stream is divided into two streams passing on opposite sides of the barrier, one stream being directed towards the upwardly moving mass and containing a sufficientv quantity of the charge as to fill the space between the barrier andthe ascending portion of the charge and the other portion havinga free drop onto the lower portion of the char e. Y

8. The met 6d herein described which consists in elevating a mass composed of materi-alto be pulverized and crushing bodies,

causing the elevated portion of the mass to divide in separate streams, one in contact "with the upwardly moving mass to efiect reduction by attrition and the other stream falling clear or out of contact with the upwardly moving mass, efi'ecting reduction by attrition and impact at an intermediate point of such second stream and removing the pulverized material as formed at a int adjacent to-that atawhich such secon re, d ction is efiected.

contact with the upwardly movingmass and one out of contact therewith, so interposing a barrier in the path of movement of the latter stream that reduction of material in said stream is effected by impact and attrition and introducing material to be reduced into the charge at a point below the barrier and distributing such material from end to end' of the interior of the charge by means of a stream of air.

-10. The method herein described which consists inelevating a mass composed of material to be pulverized and crushing bodies, causing the elevated portion of the mass to descend in separate streams one out of contact with the upwardly moving mass and one in contact therewith, effecting reduction of material in the first stream by impact and attrition, causing a stream of material-laden air' to enter the charge at one end and passing between the two descending streams, escape laden with pulverized material from the opposite end of p the charge. p

11. The method herein described of reducing material which consists in imparti'ng to a mass of material to be reduced and crushing bodies harder than such material, an upward movement about an axis of rotation to a point dependent on the rate of rotation, causing the body of material falling from such point to move in diverging paths thereby 'forminga pocket or cavity in said mass below the axis of rotation, supplying material to be reduced at a point on the same side of the axis of rotation as the pocket or cavity and causing currents of air for segregation purposes to flow through portions of the mass into the cavity and thence longitudinally ofthe axis of rotation.

12. A grinding mill of the ball and drum type having in combination a rotatable drum having hollow trunnions, means for continuously falling material to be reduced in one end of the drum, means for causing a continuous flow of air through one trunnion and out through the opposite trunnion and an axially arranged barrier having an ex ternal diameter notsubstantially less than one-fourth of the internal diameter of the drum whereby such a percentage of the falling portion of the charge in the drum is diverted to the -space between the boiler and the ascending portion of the charge in the drum, as to fill such space.

13. A grinding mill of the drum and ball type having in combination a rotatable drum having hollow 'tr'unnions, means for material to bereduced through one trunnion, in respectively on opposite sides of the a cylindrical screen having an external diamcy indrical screen. 7 eter not substantially less than one-fourth In testimony whereof I have hereunto set 1 the internal diameter of the drum projectmy hand this first day of March, 1923, at

5 ing inwardly into the drum from the other Pittsburgh in the county of Allegheny and trunnion and adapted to separate falling State of Penns lvania. portion of the charge into two streams pass- EANIEL V. SHERBAN. 

